Why the Aviation Industry Operates on 400 Hz Power

Updated: September 14th, 2016

The idea of making electricity useful for commercial lighting and motors initiated an argument. One side wanted direct current (DC). One wire will always be positive (+) and the other wire is always negative (-).

The other side supported alternating current (AC). In this system, the voltage is constantly moving between positive and negative. The shape of this changing voltage is a sine wave.

The changing AC voltage provided the advantage of using transformers to change the voltage. High voltage at low amps could be sent long distances over small wire, and then transformed to a safe lower voltage for distribution inside a home or factory.

Once the decision was made to use AC, the next question was, how fast should the voltage change? How many cycles per second (Hertz, Hz) should be produced?

As the frequency of the voltage change was made slower, the size and weight of the transformers and generators increased and became more expensive. As the frequency was made faster, more power was lost in the transmission lines, which also increased cost.

The most economical frequency for the power company was around 60 cycles per second. Some countries standardized on 50 cycles per second or Hertz (Hz).

When aviation began using electricity, it was DC power. As AC became more prevalent in aircraft, the primary concern was the size and weight of transformers, motors and power supplies. The idea was proposed to use a higher frequency to make the components lighter, since the length of power transmission was small, the increased power loss would be negligent.

A special generator was designed to create an output of 400 Hz. This allowed a motor which was the size of a watermelon to be replaced by one the size of a one-pound coffee can which could do the same work.

The saving of weight allowed increased cargo capacity and decreased fuel consumption. Power at 400 Hz for aviation was a success and became the standard of modern AC-powered aircraft.

Airports all around the world standardized on the same power system. This included the physical plug and cable as well as the 400 Hz power so that aircraft from anywhere in the world could land and be serviced wherever they landed.
The aviation power system of 400 Hz became one of the first worldwide-adopted standards.

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